Potassium–sodium niobate lead-free piezoelectric ceramics: recent advances and perspectives

Potassium–sodium niobate lead-free piezoceramics have received considerable attention for replacing lead-based ones in some practical applications. This review covers the fundamental aspects of potassium–sodium niobate lead-free piezoelectrics in terms of the relationships between new phase boundaries and high piezoelectric activity. The enhancement in its piezoelectric response is primarily concerned for piezoelectric devices. For a potassium–sodium niobate material, the phase boundaries modifications are important to achieve a high piezoelectric activity. In addition, the compositions concerning phase boundaries have a significant impact on the intensities of piezoelectric properties. Correct evaluation of piezoelectric properties is becoming more important in enabling an accurate comparison of a number of studies based on different systems. In the latter part, our recent advances in its piezoelectric properties are presented with a focus on potassium–sodium niobate to give an overview of the various problems and solutions.